1. Field of the Invention
The present invention relates to a modem control apparatus, control method thereof, and storage medium.
2. Description of the Related Art
An AT modem is that which incorporates a controller, and is of a type which makes modem control by an AT command set. The AT command set is the world's most popular modem command system advocated by Hays Microcomputer Products, U.S.A. Using commands starting with “AT (Attention)”, the controller can easily operate all of modem sending and receiving functions. Note that Japanese Patent Laid-Open No. 10-042062 has proposed a method of switching a modem mode between those at the times of dialing and communications upon making data communications between terminals using AT modems.
It is difficult for an AT modem to execute flexible control that requires realtimeness required for facsimile (FAX) communications unlike in a controller-less type modem for which a controller on the apparatus side executes thorough modem control. AT modems are popularly adopted as data modems for PCs, but they are not adopted very much as FAX modems. For this reason, when an AT modem is used, control required for FAX communications cannot often be accurately executed.
For example, T0 timer control at the time of FAX sending is one of such difficulties. In this case, a T0 timer measures a reception waiting time of a procedure signal from a partner apparatus of a FAX communication after completion of dialing of a partner telephone number. The T0 timer is specified by approval tests of respective countries, and if it is not accurately controlled, approval cannot be received. Therefore, accurate control of the T0 timer is very important. In the AT modem, an AT command used to execute dialing is “ATD”. Immediately after reception of this command (before a dial number is output onto a line), the AT modem returns a result. Hence, a controller on the apparatus side (CCU: Communication Control Unit) cannot correctly detect a dialing end timing, and the T0 timer cannot be accurately measured. For example, when a dial number of 20 digits is output onto a pulse line of 10 PPS, 20 sec or more are required at a maximum. Since a time required to output a dial number changes considerably depending on a line type (tone or pulse) and the number of digits of the dial number, the standard cannot often be satisfied if the measurement of the T0 timer is started from the issuance timing of the ATD command.
As a feature of the AT modem, when a dial command is issued, an output of a calling tone (CNG) is automatically started after completion of dialing, and a FAX procedure unwantedly begins. This means that the CCU cannot control the CNG output timing. At the time of occurrence of a communication trouble, it is very effective to control the CNG output timing. However, the AT modem cannot change the CNG output timing, thus posing a problem.
Note that Japanese Patent Laid-Open No. 10-042062 above cannot solve these problems since it can only switch a modem mode between those at the times of dialing and communications.